Tool controlling fluid valve



Jan. 6, 1953 c. JOHNSON 2,624,540

TOOL CONTROLLING FLUID VALVE 2 Sl-lEETS-SHEET 1 Original Filed March 2, 1944 ISnmmot CLARENCE JOHNSON FIG. 5 wW Jan. 6, 1953 c, JOHNSON 2,624,540

TOOL CONTROLLING FLUID VALVE 2 SHEETS-SHEET 2 Original Filed March 2, 1944 M PUMP SUMP FIG. 2

Zmventor CLARENCE JOHNSON m/ Z/MMM Patented Jan. 6, 1953 TOOL CONTROLLING FLUID VALVE Clarence Johnson, Orfordville, Wis., assignor to Bailey Meter Company, a corporation of Dela- Ware Original application March 2, 1944, Serial No. 524,707, now Patent No. 2,475,326, dated July 5, 1949. Divided and this application September 3, 1948, Serial No. 47,615

Claims.

This invention relates to duplicators for controlling the operation of a material forming machine so that a work piece is formed to a contour or configuration determined by a template, pattern or cam.

One of the objects of my invention is to improve the sensitivity of contour control of the type described and to thereby increase the accuracy with which the work piece is formed.

A further object of my invention is to provide a contour control of materially simpler construction than those now available.

In accordance with my invention the template or cam for producing the desired configuration on the work piece is scanned by a tracer regulating a jet of fluid from a nozzle. Variations in the shape of the template cause corresponding changes in the fluid discharged from the nozzle which variations are then used to control the relative positioning of the tool and work piece.

Further, in accordance with my invention the changes in fluid pressure control the relative positioning of the tool and work piece through a hydraulic relay and servo-motor, to the end that ample power is available for accurately positioning the tool relative to the work piece, or vice versa. The relative rates of movement of the tool and work piece in two or more directions are simultaneously controlled so that the rate of cutting feed of the tool remains substantially constant regardless of changes in contour or profile of the template, pattern or cam.

Certain structures and apparatus disclosed herein are claimed as my invention. Other features and apparatus, disclosed but not claimed herein, are disclosed and claimed in the copending application Serial No. 524,705 of Frederick A. Barnes filed March 2, 1944, now Patent 2,486,097 of October 25, 1949, and having the same assignee. This application constitutes a division of my copending application Serial No. 524,707 filed March 2, 19%, now Patent 2,475,326 of July 5, 1949.

Obviously a duplicator or contour control of the type forming the subject matter of my invention may be employed with material forming machines or machine tools of various types, such as milling machines, lathes, slotters, planers, die sinking machines and other machines in which the relative feed between the tool and work may be suitably controlled. By way of example I illus- Fig. 1 is a plan view of an engine lathe illustrating the application of my invention thereto.

Fig. 2 is a diagrammatic illustration of the pneumatic and hydraulic control circuits employed in the embodiment of my invention shown in Fig. 1.

Fig. 3 is a transfer valve arrangement of Fig. 2.

Fig. 4 is a front elevation, partly in section, of a fluid resistance assembly of Fig. 2.

Fig. 5 is an enlarged sectional elevation of the fluid resistance of Fig. 4.

Fig. 6 is a modification of Fig. 5.

Fig. '7 is an isometric view of the movable element of the fluid resistance of Fig. 5.

Fig. 8 is an isometric view of a modification of Fig. '7.

Fig. 9 is a sectional view in the direction of the arrows along the line 9-9 of Fig. 8.

As is well understood by those familiar with the art, in some machine tools such as lathes, the tool is moved longitudinally and transversely of the work piece which, except for rotation about its center, remains stationary. In other machine tools, such as some types of milling machines, the work piece may be moved in two directions, while the tool, except for rotation about its axis, remains stationary. In some other types of milling machines, and usually in die sinking machines, the tool may be moved in one or more directions and the work piece may also be moved in one or more directions. In all instances it will be observed, however, that it is the relative movement between the tool and work piece that causes the work piece to be formed to a desired shape. As one specific embodiment I have chosen to illustrate and describe my invention incorporated in a lathe wherein the work piece, except for rotation about its center,

remains stationary and the tool is moved transversely and longitudinally thereof. It will be evident that my invention is applicable to a wide variety of machine tools, and that when I speak of relative movement between the tool and work piece I include either an arrangement where the tool is stationary and the work piece is moved, or where the work piece is stationary and the tool is moved, or a combination of the two.

Referring now to Fig. 1, I show my invention applied to an engine lathe i having a head stock 2 adapted to be rotated by any suitable means. The carriage i is movable longitudinally along the bed of the lathe in suitable ways 5 and supports the tail stock 3. Also movable 1ongitudi nally along the bed of the lathe in suitable ways 6 is a carriage '2 upon which is mounted a cross- 3 slide 8 movable on ways transversely of the bed of the lathe.

The cross-slide 8 is provided with an adjustable tool support 9 in which is secured a tool [0. Transverse movements of the tool is are produced through the agency of a hydraulic cylinder H having a piston l2 adapted to position the crossslide 8 through the agency of a piston rod l3. Longitudinal movements of the tool If), that is movements of the tool parallel to the bed of the lathe in a longitudinal direction, are produced by means of a hydraulic cylinder l4 having an operating piston rod l5.

Supported by the head stock 2 and the tail stock 3 is a work piece I6 which, for illustrative purposes, is shown as being formed to a parabolic shape by the tool it. This particular shape has no significance, it being apparent as the description proceeds that by my invention the work piece may be formed automatically to any desired contour. The master template or cam I! is rigidly held in parallelism to the work piece l6 upon any convenient extension ill of the lathe bed. The profile of the master template I! is the contour which it is desired to reproduce upon the work piece It. In Fig. 1 the shape of the work piece [6 follows in general a parabolic function merely as an example. For contacting and following the profile of the master template I! I provide a tracer assembly I!) rigidly mounted on 1 and movable with the cross-slide 8. The tracer assembly I9 is shown in larger and more detailed fashion in my above mentioned Patent No. 2,475,326 as having a vertical extension adapted to contact the front edge or profile of the master template ll. A body member or housing is adjusta-bly mounted to the cross-slide 8 and the tracer extension or arm 20 is carried with the body.

The tracer arm 26 continually scans the profile of the template l? and controls the bleed to atmosphere of a substantially constant pressure supply of compressed air. The variable bleed or rate of flow of air to the atmosphere produces corresponding changes in back pressure or pressure of the air efiective to cause a positioning of the piston rods l3 and [5 for transverse and longitudinal movements respectively of the tool [0.

In Fig. 2 I have shown diagrammatically the pneumatic and hydraulic circuits for controlling the servomotors H and M by the tracer I9 in such manner that the motor II will position the cross-slide and consequently the tool H) transversely of the lathe, or in other words toward or away from the work piece I6 as the tool is traveling longitudinally. The action is such that if the contacted edge of the master template I l is a straight line parallel to the axis of the work piece 16, then the work piece l6 would be turned to cylindrical form. If the contacted edge of the template ll is a straight line, out inclined relative to the axis of the work piece I 6, then the work piece it will be shaped to a taper. The particular showing of Fig. 1 is in general a para bolic curve on the contacted edge of the template l1, and thus the form which is to be produced on the work piece i5.

Air under pressure from any convenient source is passed through a pressure regulator 22 and volume chamber 23 to a header 24, from which a branch 25 leads through an orifice 25 to the tracer assembly l9. As the discharge from the tracer H] to the atmosphere varies, the pressure in the branch 25 between the orifice 26 and the tracer assembly 19 will vary, and such controlled air pressure, representative of changes in contour of the template H, is effective upon a bellows 2'! of a pilot valve assembly 28 and simultaneously upon a bellows 29 of a fluid resistance assembly 38. The pilot valve assembly 28 is explained in my Patent 2,526,361 while the fluid resistance 36 will be explained more in detail in connection with Figs. 4-9 inclusive herein.

I show an oil pump 3! driven by a motor 32 and drawing its supply of oil from a sump 33. Oil under pressure is supplied the pilot valve 23 by thhe pump 3! through a pipe 34. From the pilot valve 28 oil is supplied to one end or the other of the hydraulic motor I! through the pipes 35 or E'l. Drainage from the pilot 28 is returned to the sump 33 through a pipe 3?. In the pipe 36 I show a hand adjustable valve 38 for variably throttling the flow of oil therethrough and thus controlling the basic rate of travel of the piston rod l3. Within any preselected range of speed of piston travel the relay of the assembly 23 not only controls the direction of piston travel but the speed within said range.

In connection with the hydraulic motor I 2 and adjustable fluid resistance assembly 33 I provide switching valves 3:9 and 43 arranged to be moved together to either a normal or a rapid traverse position of operation of the hydraulic motor it. The valves and are shown in 2. in the normal operating position. Oil under pressure from the pump SI is forced through a pipe 4!, the valve 53 and a pipe 43 to one end of the hydraulic motor it. Oil from the other end of the motor passes through a pipe 32, the valve 40, the valve 38, the pipe Mi, the adjustable fluid resistance 32?, and the pipe 45 to the sump 33. The regulation of the variable resistance 30 determines the rate of flow of oil through the pipe 42, and consequently the rate of travel of the piston rod 55 toward the left in the drawing. Thus the rate of longitudinal travel of the tool I0 along the Work piece is controlled by the variable resistance 30 to passage of oil therethrough from the left-hand end of the motor 1 3.

In Fig. 3 I show a passage relation of the switching valves 39, 4G for a rapid return" of the piston rod 55 from left to right of Fig. 2. That is for a rapid return of the too] i to the beginning of its working travel. Oil from the pump 3! passes directly through the pipe 4!, the valve 40, and the pipe 42; while oil from the right-hand end of the mo'wr I l passes directly hrough the pipe 43, th valve it, the valve 39, to the pipe 45 and sump 33. Thus on the rapid return of the piston rod ii? there is no throttling of its speed of travel by the variable resistance 30, and thus the tool is traversed to the right at maximum speed.

In general, the operation of the system illustrated in Figs. 1, 2 and 3 is as follows. The air pressure established within the pipe 25 is such that, the bellows 2'! and (and the movable parts of the assemblies 23, 36 positioned thereby) provide a normal condition of operation. The pilot valve assembly 23 looks oil from the pipes 35, 36 so that the piston rod i3 is not moving and the tool If] travels a cutting path parallel to the axis of the work piece it. At the same time the variable fluid resistance is in a position to provide a normal speed of travel of the piston rod I5 from right to left on the drawing, thus moving the tool it alon the work at a uniform normal speed.

If the profile of the template ll recedes from the axis of the work piece, or advances toward the axis of the work piece, the air pressure within the pipe 25 is correspondingly varied in proper direction to increase or decrease the air pressure within the bellows 2'! and 29 and to cause a corresponding positioning of the movable elements of the pilot valve 28 and fluid resistance 30. Such movement causes the hydraulic motor i I to position the tool toward or away from the axis of the work piece l6, and thus reproduce upon the work piece IS the contour of the master template i1. At the same time any departure (in either direction) of the movable element of the variable resistance 30 from normal position will increase the resistance to oil passage therethrough and tend to slow up travel of the piston rod I5. Thus longitudinal travel of the tool H] from right to left on the drawing will be at a speed slower than the normal speed depending upon the rate of travel of the tool 50 toward or away from the axis of the work piece It. If, for example, the profile of the template l1 includes a shoulder at right angles to parallelism with the axis of the work piece 16, then there will be a complete stoppage of longitudinal travel of the tool Ill while the tool is advancing directly toward the axis of the work piece or is receding directly therefrom. Movement of the tracer arm 20 either toward or away from the contact edge of the template H from a neutral or normal position results in a decrease in speed of travel of the tool IE1 in a longitudinal direction from its normal speed of travel and irrespective as to whether the tool is advancing toward the axis of the work piece or is receding from the axis.

After complete travel of the tool has been ac-- complished from right to left, then a rapid return of the tool to the right may be accomplished by moving the switching valves 39, 49 to the posi tion shown in Fig. 3 wherein the connections to the cylinder l4 are reversed and the variable restriction 30 is made non-cilective.

The system which I have just described in connection with Figs. 1, 2 and 3 is in general a twoelement control wherein the lathe tool is posi- A 'tioned both transversely and longitudinally of the work piece. It will, of course, be seen that either element may be employed. without necessarily employing the second element. For example, a lathe or similar material forming machine may have the tracer assembly l9 control only the cross feed of the tool or only the longitudinal speed of the tool, or the two combined as I have just described. It may, however, in certain instances be desirable to include a third element, namely, a control of the speed of rotation of the work piece l5, so that the linear cutting speed of the tool will remain constant regardless of the diameter of the work piece at which the tool is cutting. In other words, so that the speed of rotation of the work piece it will be different when the tool I8 is cutting at a larger diameter than it is when the tool is cutting at a smaller diameter. To illustrate such a possibility I have indicated on Fig. 1 an oil motor at for rotating the work piece l6 and under the control of a tracer assembly I9A which may be mounted on and longitudinally moved with the carriage 1. On the cross-slide 8 I locate a cam surface 4'! movable with the tool it! and relative to the tracer arm 20A of the tracer assembly ISA so that the tracer arm 20A is deflected by the cam 41 an amount indicative of the transverse position of the tool 10 relative to the axis of the work piece 96.

As explained in connection with Fig. 2, the

tracer assembly 19A ma control a variable fluid restriction A in the supply line 48 leading from the pump 3| to the motor 46, or in the discharge line 69 between the motor 46 and the sump 33, so that the speed of the motor 46 will depend entirely upon the position of the tracer arm 20A relative to the assembly I9A, and consequently will depend upon the transverse location of the cutting tool In. The tracer assembly ISA is connected to the air header 24 through abranch 50 and. applies a regulated air pressure to the bellows 5| of the fluid restriction assembly 30A, such pressure bearing a definite relation to the transverse position of the tool l0 relative the axis of the Work piece 15.

In other words, as the diameter at which the tool I0 is cutting increases or decreases, the speed of rotation of the work piece It will correspondingly decrease or increase respectively. It will be apparent that this third element of control may be included on the lathe of Figs. 1, 2 and 3, either alone or in combination with either or both of the two elements of transverse and longitudinal tool travel.

The tracer assembly I9 is described in detail in the above referred-to Barnes Patent 2,486,097.

With the arrangement so far described there are three basic conditions of operation, viz.

1. For cylindrical turning where the profile of the template I! is a straight line parallel to the axis of the work piece IE5. Upon air pressure being available at the pipe 25, and correspondingly within the bellows 2'! and 29, the piston 12 (Figs. 1 and 2) moves toward the top of the drawing carrying the tool It into engagement with the work piece and causes the tracer arm 2% to engage the edge of the template I! and deflect. This permits a predetermined bleed of air to the atmosphere and a predetermined pressure of air imposed within the bellows 21 and 29. At this predetermined air pressure the pilot valve assembly 28 is so positioned as to lock oil in the pipes 35, 36 to opposite ends of the piston l2 and prevent the tool I0 from further advancing toward or receding from the axis of the work piece It. At the same time the air pressure imposed upon the bellows 29 causes a predetermined normal flow of oil through the pipe 42, the valve 40, the valve 39, the pipe 44, the resistance 30 and the pipe 45 to the sump 33, resulting in a normal uniform rate of travel of the piston rod I5 from right to left, and correspondingly a normal uniform rate of travel of the tool 10 from right to left along the work piece I6. The result is a cylindrical turning of the work piece It.

2. Assume that the profile of the template I! recedes from parallelism with the axis of the Work piece 16. The deflection toward the left of the tracer arm 28 is eased, the valve assembly tends to move toward the left, and pressure with in the pipe 25 tends to build up. Such increase in pressure effective upon the bellows 21 causes a fiow of oil through the pipe 36 and a bleed of oil through the pipe 35, resulting in a movement of the piston rod [3 (upward in Fig. 1) such that the tracer arm 20 will tend to follow the receding profile of the template ll and at the same time the tool. it will move toward the axis-of the work piece Hi. If the recession of the template ll is uniform, that is a straight line departing from the axis of the work piece l6, then the work piece will be formed to a taper of decreasing diameter toward the left. The increase in air pressure within the pipe 25 effective upon the bellows 29 causes the variable fluid resistance 30 to tend to throttle the discharge of oil from the left-hand end of the cylinder I4, and reduce the speed of longitudinal travel of the tool toward the left.

3. If the profile of template I 1 tends to approach the axis of the work piece IS the reverse condition obtains, namely, that the tracer arm 20 tends to deflect in a greater degree toward the left, tending to decrease the air pressure within the pipe 25. Such decrease in air pressure effective upon the bellows 21 results in a movement of the piston rod I3 downward on the drawing (Fig. 1), resulting in the tool I0 producing an increasing diameter upon the work piece I 6. At the same time the decrease in pressure within the pipe 25 effective upon the bellows 29 causes the variable fluid resistance 30 to throttle the discharge of oil from the lefthand end of cylinder I4, and thus reduce the longitudinal travel speed of the tool I0.

It will be observed that under condition 2 as well as under condition 3, namely, when the tool I 0 is positioned either toward or away from the axis of the work piece I6, the rate of longitudinal travel of the tool is decreased. To carry this to an extreme, assume that the profile of the template I! includes a shoulder normal with the axis of the work piece, the longitudinal travel of the tool I0 will cease, while the tool is approaching or receding from the axis of the work piece along a line normal thereto. For all degrees of taper or inclination relative to the axis of the work piece, a corresponding rate of longitudinal travel of the tool is obtained. Thus in cutting a step taper a different longitudinal speed is had than in cutting a slow taper.

The adjustable fluid resistance assembly 3!! is illustrated in greater detail in Figs. 4-9 inclusive. Therein I have indicated by the same numerals those parts which are similar in the relay 28. The assembly 35 of Fig. 4 is shown as approximately one-half scale whereas Fig. 5 is approximately full scale, while Figs. 7, 8 and 9 are to further enlarged scale.

The adjustable fluid resistance comprises a movable member III! positionable relative to a stationary sleeve III. The two are confined in a fixed housing H2 joined by inlet pipe 44 and outlet pipe 45. Member II ll is provided with spaced lands H3, H4 having pressure equalizing grooves. In neutral position (as shown in Fig. 5) the lands are so spaced and located relative to access to the pipes 44, 45 that what may be considered a normal flow of oil exists from the pipe 44 to the pipe 45. The power system, including the spring 88 and bellows 29 may be so adjusted that the member H0 will be in its normal position for a given air loading pressure efiective upon the bellows 29 which will be the neutral pressure for the relay valve Fig. 4. Any departure of such air pressure, either an increase or a decrease, resulting in movement of the member H0 upwardly or downwardly relative to the sleeve III, will cause a decrease in rate of oil passage from the pipe 44 to the pipe 45. Thus any variation in air loading pressure upon the bellows 29 will result in a slowing down of the travel of the piston rod I5 from right to left as compared to its normal speed of travel. This is the same thing as saying that the longitudinal travel of the tool I0 will be decreased in speed upon any movement of the tracer arm 20 from neutral or normal position Lil 8 corresponding to a normal air pressure in the pipes 25 and I09.

In order that the value of what I term a normal rate of passage of oil from pipe 44 to pipe 45 may be basically changed, I provide means for angularly moving the member III) to thereby increase or decrease the opening to oil flow between the pipes 44 and 45 when the member H0 is axially in its normal position. Such means includes a local or remote handle H5 adapted to cause rotation of spur gears H6, H1, the latter being loosely journaled on the body or fixed housing I I2. Carried with the gear H1 is an arm H8 having a driving post H9. Angular movement of the driving post H9 around the axis of the assembly angularly positions the member H5 and ball joint 93 through the agency of a leaf spring or crank I29. The construction is such that the member H0 and leaf spring I 20 may be moved axially without appreciable loading by the leaf spring.

In Fig. 6 I illustrate the possibility of angularly moving the sleeve HIA, through the agency of leaf spring I20, relative the axially movable member I I5 and stationary housing I I2.

Referring now to Fig. '7, it will be observed that the member H0 has a flatted portion I2I joining the lands H3, H4. Preferably the width of the rectangular cross-section portion I2I is less than the diameter of the lands H3, H4. Said lands H3, H4 are beveled toward the flatted portion l2l so that as the member no (in normal axial location) is angularly moved around its axis through the agency of the handle H5, a difierent portion of the bevel is presented opposite the exit from the pipe 44 and opposite the entrance to pipe 45. Thus in a given angular position of the niernper H3 any vertical positioning of the member is over a different range of fluid flow rate than for some other angular position.

In Figs. 8 and 9 I show a further preferred construction of the member Hi wherein that portion I22 joining the lands H3A, H 4A is cylindrical and of a slightly less diameter than the diameter of the lands. At the facing ends of lands HEA, I'I4A the step constituting the difference in diameter between the portion I22 and diameter of the lands is formed as a spiral over of the circumference, both spirals having similar angular orientation. As indicated in Fig. 9 this double spiral end of each land is milled to the depth of the diameter of the portion I22. With this preferred construction a more graded or gradual adjustment of the range of fluid passage in accordance with angular rotation of the member H0 is obtained. It will be apparent that the member I I 0 may assume other shapes to allow a greater or lesser latitude in adjustability of the range of fluid throttling, and thereby the range in speed of the piston rod I5.

While I have illustrated and described certain preferred embodiments of my invention it will be understood that they are by way of example only and that I am not to be limited thereto except as defined in the following claims.

What I claim as new, and desire to secure by Letters Patent of the United States, is:

1. In a hydraulic flow control valve, the combination comprising a housing, a sleeve mem ber mounted to said housing and provided with longitudinally spaced fluid ports, a reciprocable fluid resistance stem member axially positioned within said sleeve member, said stem member being of generally cylindrical shape having lands spaced to cooperate with said ports, the portion of the stern member between said lands being reduced to form a central relatively thin rectangular cross-section the width of which is slightly less than the diameter of the lands, the said portion being joined to each land by a pair of beveled surfaces, angular movement of one of said members relative the other varying the presentation of the beveled surfaces to the ports, and means for angularly positioning the stem member relative to the sleeve member.

2. In a hydraulic flow control valve, the combination comprising a housing, a sleeve member mounted in said housing and provided with longitudinally spaced fluid ports, a reciprocable fluid resistance stem member axially positioned within said sleeve member, said stem member being of generally cylindrical shape having lands spaced to cooperate with said ports, the portion of the stem member between said lands being reduced to form a central relatively thin rectangular cross-section the width of which is slightly less than the diameter of the lands, the said portion being joined to each land by a pair of beveled surfaces, angular movement of one of said members relative the other varying the presentation of the beveled surfaces to the ports, and means for angularly positioning the sleeve member relative to the stem member.

3. In a hydraulic flow control valve, the combination comprising a housing, a sleeve member mounted in said housing and provided with longitudinally spaced fluid ports, a reciprocable fluid resistance stem member axially positioned within said sleeve member, said stem member being of solid generally cylindrical shape having lands spaced to cooperate with said ports, the portion of the stem member between said lands being cylindrical and of a slightly less diameter than said lands, the facing ends of said lands being formed as similarly oriented spirals extending over 180 degrees of the circumference, angular movement of one of said members relative the other varying the presentation of the end spirals to the ports, and means for angularly positioning one of said members relative to the other.

4. In a hydraulic flow control valve, the combination comprising a housing, a sleeve member mounted in said housing and provided with longitudinally spaced fluid ports, a reciprocable fluid resistance stem member axially positioned within said sleeve member, said stem member being of generally cylindrical shape having lands spaced to cooperate with said ports, the portion of the stem member between said lands being of reduced cross-section with the adjacent ends of said lands formed with oppositely disposed receding surfaces for varying the flow range controlled by axial positioning movement of the stem member, supporting means including a ball joint secured to one end of said stem member, a leaf spring fixedly secured as a crank to the other end of said stem member, and means connected to an outer part of said leaf spring and said housing for angularly positioning said stem member relative to said sleeve member.

5. In a hydraulic flow control valve, the combination comprising a housing, a sleeve member mounted in said housing and provided with longitudinally spaced fluid ports, a reciprocable fluid resistance stem member axially positioned within said sleeve member, said stem member being of generally cylindrical shape having lands spaced to cooperate with said ports, the portion ofthe stem member between said lands being reduced to form a central relatively thin rectangular cross-section the width of which is slightly less than the diameter of the lands, the said portion being joined to each land by a pair of beveled surfaces, angular movement of one of said mem bers relative the other varying the presentation of the beveled surface to the ports, supporting means including a ball joint secured to one end of said stem member, a leaf spring fixedly secured as a crank to the other end of said stem member, and means including gearing for driving an arm connected to an outer part of said leaf spring for angularly positioning said stem member relative to said sleeve member.

CLARENCE JOHNSON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 26,654 Cridge Jan. 3, 1860 685,510 Flint Oct. 29, 1901 701,574 King June 3, 1902 2,059,363 Kimball Nov. 3, 1936 2,141,428 Carroll Dec. 2'7, 1938 2,158,737 Wunsch May 16, 1939 2,311,108 Hauser Feb. 16, 1943 FOREIGN PATENTS Number Country Date 113,405 Sweden of 1945 

